Understanding API security is crucial as APIs form the backbone of modern interconnected applications, making them prime targets for cyberattacks. Drawing on nearly 30 years of cybersecurity experience and an extensive background in network security and forensic analysis, this book provides the knowledge and tools to strengthen your API security practices and protect against cyber threats comprehensively. This book begins by establishing a foundational understanding of APIs, particularly focusing on REST and GraphQL, emphasizing their critical role and potential security vulnerabilities. It guides you through setting up a penetration testing environment to ensure the practical application of concepts. You’ll learn reconnaissance techniques, information-gathering strategies, and the discovery of API vulnerabilities. Authentication and authorization testing are thoroughly explored, covering mechanisms, weaknesses, and methods to bypass security controls. By comprehensively addressing these aspects, the book equips you to understand, identify, and mitigate risks, strengthening API security and effectively minimizing potential attack surfaces. By the end of this book, you’ll have developed practical skills to identify, exploit, and secure APIs against various vulnerabilities and attacks.